One problem that machine designers often face is the transfer of rotary motion from one shaft to another when the shafts are not aligned. The classic universal or Hookeâs joint (Model P-1) is such a mechanism but suffers the property that constant motion on the input shaft produces a non-steady motion on the output shaft. The jointed coupling in Model P-3 uses a symmetric joint to remove the irregularity in motion. This can be seen by measuring the input and output increment angles attached to the two cranks on the model. The model was also designed by Reuleaux to show that if the joint is not operated in a symmetric manner, irregular motion results. Reuleaux cited a patent of Clemens of November 10, 1869 in the 4th edition of The Constructor.